The present invention relates to a slim motor and a device, e.g. a portable information device, mounting the same motor. More particularly, it relates to an innovative motor structure allowing to reduce a diameter of the motor, and a device mounting this motor thereby downsizing itself.
Portable devices include portable audio and video devices such as a headphone stereo player, a portable digital versatile disc (DVD), and portable information devices such as a cellular phone. A motor is used as a power source of the portable audio and video devices, and another motor is used as a vibration generator of the portable information device to inform a user of a call with tactile vibrations. In the markets of those products, downsizing and weight reducing are critical criteria to get a greater market share. In the market of portable information devices, among others, fierce competition is going on to achieve a target of xe2x80x9cthinner by one millimeter than others.xe2x80x9d This market situation entails a severe request to the motor to be slimmer and slimmer.
Japanese Patent Publication No. 2761175 discloses one of the motors adequate for the portable information device. This motor is a cylindrical core-less motor generating vibrations and mounted to a cellular phone. As shown in FIG. 8, shaft 74, bearings 75, 76, and bearing holder 77 are separately disposed in an axial direction with respect to magnet 71, rotor coil 72 and housing 73. In the motor having this structure, three elements, namely, the magnet, coil and housing, are disposed concentrically in the radius direction. The shaft, both the bearings and the bearing holder are also disposed concentrically in the radius direction.
The diameter of this motor can be reduced because two sets of three elements disposed in the radius direction are aligned. However, as shown in FIG. 8, this structure not only makes shaft 74 shorter but also makes itself complicated. Therefore, when side pressure is applied to shaft 74, load to the shaft increases, which inclines the motor to consume more current and tends to tilt the shaft. As a result, the motor may invite lowering quality and reliability. Further, since the shaft tends to tilt, an annular space between magnet 71 and coil 72 is obliged to be wide as a countermeasure against the tilt, and this lowers motor""s efficiency. In addition, the complicated structure of the motor lowers the productivity, which increases the manufacturing cost.
The easiness of shaft""s tilting is described hereinafter. As shown in FIG. 8, an axial length of coil 72 is twice as long as the space between bearings 75 and 76. Thus a tilt of shaft 74 produced at the bearings is approx. doubled to a displacement of the coil in a radius direction. This problem is essential to the motor having such a structure. In order to deal with this problem, countermeasures are required such as increasing accuracy or rigidity of the bearing, and widening a space between the coil and the magnet or the housing for preventing these elements from touching with each other.
Japanese Patent Publication No. 2789447 discloses another example. This motor generates vibration and is mounted also to a cellular phone. As shown in FIG. 9, this motor is different from the motor discussed previously because a shaft of this motor extends through a magnet, and yet it tries to reduce the diameter thereof.
In FIG. 9, lower section 81a of pipe-like bearing house 81 extends from a lower end of magnet 82, and bearing 83 is mounted to an outer wall of lower section 81a. Thus bearing 83 is disposed outside magnet 82, therefore, an outer diameter of the motor slims down by the thickness of the bearing.
As such, the magnet and bearing are aligned in the axial direction. This construction allows the outer diameter of the motor to be slim. In this construction, a shaft is so long enough in the axial direction that no such a problem discussed previously occurs.
In this construction, however; magnet 82, bearing 83 and mounting section 83a are aligned within a length of rotor coil 84 in the axial direction. Therefore, magnet 82 must be shortened by the total length of bearing 83. Thus coil 84 has a non-active section which does not interlink with magnetic flux from magnet 82, which lowers the efficiency of the motor.
In the two conventional cases discussed above, the magnet and the bearing are disposed separately so that the two elements are not overlaid in the axial direction, thereby slimming down the motor. Indeed, the shift of both the elements in the axial direction is advantageous for slimming down the motor, but this structure invites the problems discussed above.
When a cylindrical motor, as a vibration generator, is mounted to a portable device, not only slimming down the motor per se, but other peripheral elements such as a holder of the motor and an eccentric weight should be taken into consideration. Then an overall shape must be decided at an optimum balance of all the elements. Otherwise, it is not possible to obtain a thin motor producing greater vibrations with lower power consumption.
The present invention addresses the problems discussed above and aims to provide a motor having a structure allowing further slim down thereof, and thereby contributing to downsizing as well as weight reducing a device to which the motor is mounted.
The motor of the present invention comprises the following elements:
(a) a frame;
(b) a pipe disposed in the frame and fixed coaxially with the frame;
(c) a magnet of which inner wall fits in the pipe;
(d) a coil facing an outer wall of the magnet via an annular space;
(e) a shaft disposed coaxially with the magnet and the coil, and coupled to the coil;
(f) a first bearing disposed at the end of the frame and journaling a first side of the shaft; and
(g) a second bearing (inside bearing) disposed inside the frame and journaling a second side of the shaft.
A length of the magnet is such that a lower end of the magnet overreaches a lower end of the pipe, and the second bearing is disposed under the lower end of the pipe thereby fixing the bearing per se on the inner wall of the magnet.
In this structure, the second bearing is aligned with the pipe in an axial direction, so that the second bearing is disposed on the inner wall of the magnet. Therefore, a length of the magnet can extend by the length of the second bearing, so that magnetic flux traveling from the magnet to the coil can increase accordingly. As a result, the motor can be slimmed down and an excellent motor efficiency can be achieved.
Another motor of the present invention comprises the following elements:
(a) a frame;
(b) a pipe disposed in the frame, fixed coaxially with the frame;
(c) a magnet of which inner wall fits in the pipe;
(d) a coil facing an outer wall of the magnet via an annular space;
(e) a shaft disposed coaxially with the magnet and the coil, and coupled to the coil;
(f) a first bearing disposed at the end of the frame and journaling a first side of the shaft;
(g) a second bearing (inside bearing) disposed inside the frame and journaling a second side of the shaft; and
(h) an eccentric weight having a weight section and a fixing section of the weight section to the shaft.
An outer diameter of the weight section is greater than that of the frame, and an axial length of the weight section is longer than that of the fixing section. An axial position of a gravity center of the eccentric weight is within an axial length of the first bearing.
This structure allows the motor to slim down while maintaining necessary vibrations with the eccentric weight of a large diameter. Most of load to the rotor is borne by the first bearing and thus little load is borne by the second bearing.
A device of the present invention has the following structure: The device mounts the motor discussed above, and the motor is mounted to the device with a holder made of soft material.
Another device of the present invention comprises the following elements:
(a) a housing;
(b) the motor discussed above and mounted to the housing; and
(c) a device board including an electric coupling section through which the coil is powered via a powering terminal exposed outside the motor frame.
These construction allow the device to downsize and reduce its weight thanks to the slim motor. As a result, a portable device with phenomenal portability is achievable. A device with the motor having the eccentric weight can be slimmed down, and has an advantage of informing its user of a calling because large vibrations are generated when the calling arrives at the device.